Most, if not all, of the IEEE 802 wireless systems are pulse-based transmit/receive systems. While the frequency of the next transmission is known in most cases, the time, length of packet, and signal strength are all unknown until a transmission occurs. Once a transmission occurs, a receiver must tune the radio frequency (RF) and intermediate frequency (IF) sections to recover the transmitted signal and to stabilize the amplifiers before the actual data in the payload is received.
This very short time needs to have all of the demodulations operating as quickly as possible. If the feedback of the recovered signal is too soon or too late, the AGC can become unstable due to incorrect feedback timing. By sending the states from an AGC state machine controller, the backend system demodulators will know exactly where the front end is with respect to the gain changes, the time constants used for the system delays, and the periods when the backend can sample the signal and report the condition of the signal (too high or too low) back to the AGC.
The systems that exist have an AGC that attempts to converge on a training signal and provides feedback but not in a robust or predictable manner since the received signal is questionable until the AGC stops making changes. The prior art
AGC circuits receive inputs from and provide inputs to the IF and RF amplifiers. There is, however, no input to or feedback from the demodulator in prior art AGC circuits.